Excess sludge treatment method

Abstract

The invention relates to the technical field of water treatment, in particular to an excess sludge treatment method which comprises the following steps: phosphorus release: feeding excess sludge rich in phosphorus into a sludge concentration unit for concentration treatment to obtain concentrated sludge; feeding a small part of concentrated sludge into a sludge cracking unit for cracking treatment to obtain cracked sludge; feeding the residual concentrated sludge into a sludge dewatering unit for sludge dewatering treatment; and circulating the obtained cracked sludge into the sludge concentration unit. According to the method, 10%-20% of the concentrated sludge is subjected to alkalifying disintegration, a carbon source released by disintegration is used as a carbon source of phosphorus-accumulating microorganisms (phosphorus-accumulating bacteria) in the total residual sludge entering the concentration tank, anaerobic phosphorus release occurs in an anaerobic environment of the sludge concentration tank, an external carbon source is not needed, and the phosphorus-accumulating microorganisms (phosphorus-accumulating bacteria) can be recycled. The low-cost and high-efficiency phosphorus release of the total residual sludge is realized through a new scheme of alkali release of phosphorus release of a small amount of concentrated sludge and anaerobic biological phosphorus release of the total residual sludge.

Description

Technical Field

[0001] The invention relates to the technical field of water treatment, and in particular to a method for treating excess sludge. Background Art

[0002] To achieve effective recovery of phosphorus in sludge, the phosphorus in the sludge (solid phase) must be released into the liquid phase as much as possible. Efficient release of phosphorus is a key step in phosphorus recovery. The existing phosphorus release technologies mainly include:

[0003] ① Physical decomposition method: Use thermal hydrolysis, ultrasound, mechanical ball milling and other methods to break the microbial cells in the sludge and release the phosphorus-containing substances inside and outside the cells into the liquid phase. Sludge thermal hydrolysis needs to be carried out under high temperature and high pressure conditions (150-190℃, 0.7-1.1MPa). It is usually used as a pretreatment process in conjunction with anaerobic digestion process. The equipment is complex, operation and maintenance are difficult, investment and energy consumption are high, and the odorous gas generated is difficult to treat. At present, there are only a few engineering application cases; although ultrasonic decomposition is highly efficient, the reaction time is short (10-60min), and the equipment is simple, it is currently mostly in the laboratory research stage due to its high power consumption. Actual engineering applications need to overcome the defect of high power consumption.

[0004] ② Chemical decomposition method: Add acid, alkali or H2O2, ozone and other chemical agents to the residual sludge to destroy the microbial cell structure and release the phosphorus-containing substances inside and outside the cells into the liquid phase. The acid-base decomposition method has the characteristics of simple process and mature technology, but the existing sludge full-scale acid-base decomposition or H2O2, ozone oxidation and other methods have high drug consumption costs and are still difficult to achieve engineering application.

[0005] ③ Biological phosphorus release method: release phosphorus through anaerobic digestion or enzymatic biological enhanced phosphorus release. Enzymatic biological enhanced phosphorus release technology has high reagent costs and is currently in the laboratory research stage; anaerobic digestion is the most widely used sludge disposal technology in engineering, with the advantages of mature technology and low operating costs, but this method has a slow phosphorus release rate, a long time (the sludge needs to be digested anaerobicly for 20-30 days), a large reaction device, and high construction investment. If you need to increase the anaerobic phosphorus release rate and shorten the anaerobic phosphorus release time, you need a sufficient carbon source. The available carbon source in the residual sludge discharged from the biochemical system has basically been consumed in the front-end biochemical system, and a large amount of carbon source is needed to meet the requirements.

[0006] ④ Sludge incineration-wet leaching process: After dehydration and drying, the sludge is incinerated into ash, and then acid and alkali are used to leach phosphorus. The phosphorus in the sludge incineration ash mainly exists in the form of combination with metals such as Ca, Mg, Fe, and Al in the ash, which cannot be absorbed and utilized by plants. In addition, the heavy metal substances in the sludge are still retained in the ash after incineration. It is also necessary to separate the phosphorus in the sludge ash from the heavy metals and convert the phosphorus into a form that can be used by plants. The process is complicated and the cost of phosphorus recovery is high.

[0007] ⑤Combination method: Use thermal hydrolysis-acid leaching, acidification-microwave radiation, ultrasound-ozone, ultrasound-alkaline hydrolysis and other combined technologies to destroy the microbial cell structure in the sludge and release the phosphorus-containing substances into the liquid phase. Compared with a single technology, the combination technology can combine the advantages of various technologies and is the trend of technological development in this field.

[0008] Among the existing sludge phosphorus release methods, part of the phosphorus released into the liquid phase by physical breakdown method, chemical breakdown method and some combined breakdown processes exists in the form of organic phosphorus compounds (organophosphorus). Organic phosphorus compounds are difficult to remove by coagulation precipitation method, and phosphorus cannot be recovered by crystallization precipitation method. If it is necessary to improve the recovery rate of phosphorus resources in sludge, it is also necessary to further increase the content of orthophosphate in the residual sludge phosphorus release liquid phase.

[0009] In summary, a waste sludge treatment method is designed which is easy to operate and can achieve efficient phosphorus release and phosphorus recovery to solve the problems existing in the prior art. Summary of the invention

[0010] The object of the present invention is to provide a method for treating excess sludge which is easy to operate and can achieve efficient phosphorus release and phosphorus recovery. The specific technical scheme is as follows:

[0011] A method for treating excess sludge, comprising a phosphorus release step;

[0012] The phosphorus releasing step comprises the following steps:

[0013] Step S1, sending the phosphorus-rich excess sludge to a sludge concentration unit for concentration treatment to obtain concentrated sludge and supernatant;

[0014] Step S2, sending the concentrated sludge with a mass or flow rate accounting for 10%-20% to the sludge decomposition unit for decomposition treatment to obtain decomposition-treated sludge; sending the remaining concentrated sludge to the sludge dehydration unit for sludge dehydration treatment to obtain dry sludge and sludge dehydrated liquid;

[0015] Step S3, circulating the cracked sludge obtained in step S2 to the sludge concentration unit in step S1.

[0016] Preferably, the step S3 also includes a pH adjustment step, specifically: the sludge after the cracking treatment in step S2 is sent to the pH adjustment unit for pH adjustment to obtain the pH-adjusted sludge, and then the pH-adjusted sludge is circulated to the sludge concentration unit in step S1; the control range of the pH value in the pH adjustment unit is 9-10; the control range of the pH value in the sludge cracking unit is 10.8-11.5; the cracked sludge in step S3 is mixed with the phosphorus-rich residual sludge and transported to the sludge concentration unit through a pipeline for a flow time of not less than 3 seconds.

[0017] Preferably, the concentration time of the phosphorus-rich excess sludge in the sludge concentration unit is 6-24 hours; the reaction time of the sludge decomposition unit for decomposition treatment is 20-100 minutes; the control range of the pH value in the pH adjustment unit is 9-9.5; the pH value of the decomposition-treated sludge mixed with the phosphorus-rich excess sludge in step S3 is 8-9.

[0018] Preferably, the method further comprises a phosphorus recovery step, which specifically comprises:

[0019] The supernatant obtained in step S1 is input into a phosphorus recovery unit for phosphorus recovery treatment to obtain phosphorus crystals and low-phosphorus water; or the supernatant obtained in step S1 and the sludge dehydrated liquid obtained in step S2 are input into a phosphorus recovery unit for phosphorus recovery treatment to obtain phosphorus crystals and low-phosphorus water.

[0020] When the sludge dehydration unit does not use aluminum salts, iron salts, magnesium salts and other agents that can form precipitates with phosphate ions, the supernatant obtained in step S1 and the sludge dehydrated liquid obtained in step S2 are input into the phosphorus recovery unit for phosphorus recovery treatment to obtain phosphorus crystals and low-phosphorus water; when the sludge dehydration unit uses aluminum salts, iron salts, magnesium salts and other agents that can form precipitates with phosphate ions, the sludge dehydrated liquid obtained in step S2 does not enter the phosphorus recovery unit.

[0021] Preferably, the sludge concentration unit is a gravity concentration tank; the sludge concentration unit is provided with a residual sludge feed inlet, a concentrated sludge discharge outlet and a supernatant discharge outlet; the residual sludge feed inlet is connected to the residual sludge conveying pipeline;

[0022] The sludge breaking unit comprises a first shell, a first stirring assembly, a first sludge inlet pipe and a first sludge outlet pipe;

[0023] The first shell includes a first body having a first accommodating cavity, the first mud inlet pipe and the first mud outlet pipe are both arranged on the first body and are both connected to the first accommodating cavity; the first mud inlet pipe is connected to the concentrated sludge outlet of the sludge concentration unit through a first pipeline; the first mud outlet pipe is connected to the pH value adjustment unit through a fourth pipeline;

[0024] The first body is provided with a first drug adding tube communicating with the first accommodating cavity;

[0025] The first stirring assembly includes a first driving power source, a first stirring shaft and a first stirring blade. The first driving power source is arranged on the first shell; the connecting end of the first stirring shaft is connected to the output end of the first driving power source, and the free end of the first stirring shaft is arranged in the first accommodating cavity and is provided with the first stirring blade.

[0026] Preferably, it also includes a first pH controller, the first body is provided with a measuring hole connected to the first containing cavity, the first pH controller is arranged at the measuring hole to measure the pH value of the sludge; the first pH controller is connected to an external PLC control system, and the first pH controller measures the pH value of the sludge through a first measuring electrode; the first measuring electrode is arranged at the measuring hole and a protective net is provided on the outside of the measuring electrode.

[0027] Preferably, the inner wall of the first accommodating cavity is further provided with a plurality of protrusions facing the center of the first accommodating cavity; the protrusions are hemispherical protrusions with a radius of 40-80 mm; the plurality of protrusions are evenly distributed on the inner wall of the first accommodating cavity;

[0028] The first stirring shaft is provided with multiple layers of the first stirring blades at intervals along the axis direction thereof;

[0029] The first body is also provided with a first odor collecting pipe for collecting odor generated in the first accommodating chamber; the first shell also includes an opening connected to the first accommodating chamber, and a detachable cover is provided at the opening, and the first driving power source, the first dosing pipe, the first pH controller and the first odor collecting pipe are all arranged on the detachable cover.

[0030] Preferably, the pH value adjusting unit comprises a second shell, a second stirring assembly, a second mud inlet pipe and a second mud outlet pipe;

[0031] The second shell includes a second body having a second accommodating cavity, the second mud inlet pipe and the second mud outlet pipe are both arranged on the second body and are both connected to the second accommodating cavity; the second mud inlet pipe is connected to the first mud outlet pipe through a fourth pipe, and the second mud outlet pipe is connected to the residual sludge inlet through a third pipe;

[0032] The second body is provided with a second drug adding tube communicating with the second accommodating cavity;

[0033] The second stirring assembly includes a second driving power source, a second stirring shaft and a second stirring blade. The second driving power source is arranged on the second shell; the connecting end of the second stirring shaft is connected to the output end of the second driving power source, and the free end of the second stirring shaft is arranged in the second accommodating cavity and is provided with the second stirring blade.

[0034] Preferably, the phosphorus recovery unit comprises an outer shell, a middle shell, an inner shell, a water inlet pipe, a drain pipe, a discharge port, a plug flow stirring assembly, a folded plate vortex assembly, a modular vortex assembly and an inclined plate assembly;

[0035] The outer shell comprises a first cylindrical body arranged in series from top to bottom and a first conical body which is wide at the top and narrow at the bottom and closed at the lower end, a containing chamber a is arranged in the first cylindrical body, a containing chamber b communicating with the containing chamber a is arranged in the first conical body; a water collecting tank is arranged at the upper part of the containing chamber a; the middle shell comprises a second cylindrical body arranged in series from top to bottom and a second conical body which is wide at the top and narrow at the bottom and provided with an opening at the lower end, a containing chamber c is arranged in the second cylindrical body, a containing chamber d communicating with the containing chamber c is arranged in the second conical body; the upper end of the second conical body is located in the containing chamber a and the lower end thereof is located in the containing chamber b; the inner shell comprises a third cylindrical body arranged in the containing chamber c, the third cylindrical body comprises a containing chamber e with openings at both the upper and lower ends;

[0036] The e accommodating chamber forms a first water flow ascending channel; a water flow descending channel is formed between the inner wall of the second cylindrical cylinder and the outer wall of the third cylindrical cylinder; the first cylindrical cylinder and the inner wall of the first conical cylinder, the annular area between the second cylindrical cylinder and the outer wall of the second conical cylinder, and the water collecting tank form a second water flow ascending channel; the plug flow stirring assembly and the folded plate vortex assembly are arranged from top to bottom in the first water flow ascending channel; the modular vortex assembly is arranged in the water flow descending channel; the inclined plate assembly is arranged in the second water flow ascending channel; the lower part of the accommodating chamber forms a crystal aggregation area;

[0037] The water inlet pipe is connected to the supernatant discharge port, and the water inlet pipe passes through the side wall of the first columnar barrel and the side wall of the second columnar barrel and is inserted into the upper part of the first water flow rising channel, and the water outlet end of the water inlet pipe is lower than the water collecting tank; the drain pipe is connected to the water collecting tank; the discharge port is connected to the crystal aggregation area.

[0038] Preferably, the plug-flow stirring assembly comprises a third driving power source, a third stirring shaft and a third stirring blade, the connecting end of the third stirring shaft is connected to the output end of the third driving power source, and the third stirring blade is arranged on the free end of the third stirring shaft; the water outlet end of the water inlet pipe is located 20-50 cm above the third stirring blade;

[0039] The folded plate vortex assembly is located directly below the plug-flow stirring assembly, and the folded plate vortex assembly includes a first folded plate and a second folded plate arranged in parallel, the first folded plate includes a plurality of connecting plates connected in sequence, and the angle α between two adjacent connecting plates is 80°-100°; the first folded plate and the second folded plate are in a mirror image structure;

[0040] The modular vortex assembly includes a plurality of vortex monomers stacked or spaced apart, wherein the vortex monomer is a hollow columnar body formed by a first vertical plate, a second vertical plate, an upper arc-shaped outer frame, an upper arc-shaped inner frame, a lower arc-shaped outer frame and a lower arc-shaped inner frame; a vortex sheet is installed in the vortex monomer, and the cross section of the vortex sheet is at least one of a triangle, a semicircle and a rectangle;

[0041] The inclined plate assembly includes a plurality of sedimentation inclined plates arranged in parallel, and the sedimentation inclined plates are arranged at an angle with the inner wall of the a accommodating chamber; and the inclined plate assembly is located in the middle and lower part of the a accommodating chamber.

[0042] The application of the technical solution of the present invention has the following beneficial effects:

[0043] 1. The method for treating excess sludge of the present invention includes a phosphorus release step, which includes the following steps: sending excess sludge rich in phosphorus to a sludge concentration unit for concentration treatment to obtain concentrated sludge and supernatant; sending concentrated sludge with a mass or flow rate of 10-20% to a sludge cracking unit for cracking treatment to obtain cracked sludge; sending the remaining concentrated sludge to a sludge dehydration unit for sludge dehydration treatment to obtain dry sludge and sludge dehydration liquid; and recycling the cracked sludge to the sludge concentration unit. The present invention adds alkali to crack 10%-20% of the concentrated sludge, and then uses the COD (carbon source) released by the cracking as the carbon source of the polyphosphate microorganisms (polyphosphate bacteria) in the whole excess sludge entering the concentration tank, and anaerobic phosphorus release occurs in the anaerobic environment of the sludge concentration tank without the need for an external carbon source. The new scheme of alkali phosphorus interpretation of a small amount of concentrated sludge + anaerobic biological phosphorus release of the whole excess sludge realizes low-cost and efficient phosphorus release of the whole excess sludge.

[0044] 2. The present invention also includes a phosphorus recovery step, specifically including: inputting the obtained supernatant or the supernatant and the sludge dewatering liquid into the phosphorus recovery unit for phosphorus recovery treatment to obtain phosphorus crystals and low-phosphorus water. The present invention returns the sludge after alkali cracking to the sludge concentration unit, and the organic phosphorus and organic nitrogen released during the sludge cracking process are converted into orthophosphate and ammonia nitrogen that can be recovered by the subsequent phosphorus recovery unit under the action of the anaerobic environment of the concentration tank and the anaerobic microorganisms in the residual sludge, which can further improve the phosphorus recovery rate and reduce the cost of the ammonia nitrogen agent added to the phosphorus recovery unit.

[0045] 3. The sludge thickening unit in the present invention is a gravity thickening tank, which adopts the conventional gravity thickening tank in the prior art. When it is necessary to recover phosphorus from the residual sludge of an existing sewage treatment plant, it is only necessary to add a sludge breaking component (only 10%-20% of the total concentrated sludge needs to be broken), a phosphorus recovery unit and a matching control system, and to make corresponding modifications to the pipelines, so as to economically and conveniently realize efficient phosphorus release from sludge and efficient recovery of phosphorus resources in the existing sewage treatment plant.

[0046] 4. The sludge decomposition unit of the present invention comprises a first shell, a first stirring assembly, a first sludge inlet pipe and a first sludge outlet pipe, and has a simple structure. The equipment investment and operating costs (drug consumption, power consumption) of the sludge decomposition unit are only equivalent to 10%-20% of the existing full-volume sludge alkali phosphorus decomposition process, and the equipment footprint can also be saved. The addition of carbon source to the decomposition sludge shortens the anaerobic biological phosphorus release time of the sludge in the gravity thickening tank to 6 hours, which is only 1 / 80 of the time required for the traditional sludge anaerobic digestion process (anaerobic digestion time 20-30 days), greatly reducing the equipment investment and operating costs of sludge phosphorus release and phosphorus recovery.

[0047] 5. The phosphorus recovery unit of the present invention adopts an outer shell, a middle shell, and an inner shell to form a three-layer shell arrangement, forming a circulating flow channel formed by a first water flow rising channel, a water flow descending channel, and a second water flow rising channel. The plug flow stirring component and the folded plate vortex component are arranged from top to bottom in the first water flow rising channel, and the modular vortex component is arranged in the water flow descending channel, forming a mechanical stirring mixed crystallization + hydraulic vortex crystallization composite system. Due to its special structure, hydraulic classification is realized during operation, so that the solution is fully mixed with materials and the crystal particles are fluidized, and self-induction is realized without the need for external crystal seeds. Crystallization, the particle size of the crystal particles is larger than that of traditional stirred crystallization; the first water flow rising channel and the water flow descending channel form a water flow circulation flow channel to automatically sort the crystal particles, and the particles with large size and mass will automatically separate from the circulating water flow under the action of gravity and be discharged into the crystal gathering area, and the crystal particles with small particle size and mass continue to crystallize in the water flow circulation channel. The crystal particles collected in the crystal gathering area are larger in size and higher in purity than those of traditional stirred crystallization; the inclined plate assembly is arranged in the second water flow rising channel, which can perform secondary separation on the fine crystalline particles entrained in the water flow, thereby further improving the recovery efficiency of the phosphorus crystal particles.

[0048] In addition to the above-described purposes, features and advantages, the present invention has other purposes, features and advantages. The present invention will be further described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] The drawings constituting a part of this application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0050] Figure 1 It is a schematic diagram of the process of the excess sludge treatment method in a preferred embodiment of the present invention;

[0051] Figure 2 It is the plan layout of each device in the figure;

[0052] Figure 3 yes Figure 2 Schematic diagram of the elevation structure;

[0053] Figure 4 yes Figure 3 Schematic diagram of the structure of the sludge cracking component;

[0054] Figure 5 yes Figure 3 Schematic diagram of the structure of the medium phosphorus recovery unit;

[0055] Figure 6 yes Figure 5 A top view of the middle fold plate vortex assembly installed on the inner shell;

[0056] Figure 7 yes Figure 6 MM cross-section diagram;

[0057] Figure 8 yes Figure 5 A schematic diagram of the structure of the vortex monomer of the modular vortex assembly;

[0058] Fig. 9 yes Figure 8 A top view of

[0059] Fig.10 yes Fig. 9 NN cross-section diagram.

[0060] Among them, 1. Sludge concentration unit, 1.1. Residual sludge inlet, 1.2. Concentrated sludge outlet, 1.3. Supernatant outlet; 2. Sludge breaking component, 2.1. Sludge breaking unit, A1. First shell, A1.1. First accommodating cavity, A1.2. First body, A1.3. Protrusion, A1.4. Removable cover plate, A2. First stirring component, A2.1. First driving power source, A2.2. First stirring shaft, A2.3. First stirring blade, A3. First mud inlet pipe, A4. First mud outlet pipe, A5. First dosing pipe, A6. First pH controller , A6.1, first measuring electrode, A7, first odor collecting pipe; 2.2, pH value adjusting unit, B1, second shell, B1.1, second accommodating chamber, B1.2, second body, B2, second stirring assembly, B2.1, second driving power source, B2.2, second stirring shaft, B2.3, second stirring blade, B3, second mud inlet pipe, B4, second mud outlet pipe, B5, second dosing pipe, B6, second pH controller, B6.1, second measuring electrode, B7, second odor collecting pipe; 3, sludge dehydration unit; 4, first pipeline; 5, second pipeline; 6, first Pipeline 3; 7, Pipeline 4; 8, Phosphorus recovery unit, 8.1, Outer shell, 8.1.1, First columnar cylinder, 8.1.2, First conical cylinder, 8.1.3, A accommodating chamber, 8.1.4, B accommodating chamber, 8.2, Middle shell, 8.2.1, Second columnar cylinder, 8.2.2, Second conical cylinder, 8.2.3, C accommodating chamber, 8.2.4, D accommodating chamber, 8.3, Inner shell, 8.3.1, Third columnar cylinder, 8.3.2, E accommodating chamber, 8.4, Water collecting tank, 8.5, Water inlet pipe, 8.6, Drain pipe, 8.7, Discharge port, 8.8 , plug flow stirring assembly, 8.8.1, third driving power source, 8.8.2, third stirring shaft, 8.8.3, third stirring blade; 8.9, folded plate vortex assembly, 8.9.1, first folded plate, 8.9.2, second folded plate, 8.10, modular vortex assembly, 8.10.1, first vertical plate, 8.10.2, second vertical plate, 8.10.3, upper arc outer frame, 8.10.4, upper arc inner frame, 8.10.5, lower arc outer frame, 8.10.6, lower arc inner frame, Y, semicircular shell vortex sheet, S, isosceles right triangle vortex sheet; 8.11. Inclined plate assembly; A. First water flow rising channel, B. Water flow falling channel, C. Second water flow rising channel, D. Crystal gathering area; 9. Fifth pipeline; 10. Dry mud conveying parts; 11. Sixth pipeline; 12. Residual sludge conveying pipeline; 13. Seventh pipeline; H. Pipeline mixer, H1. Magnesium salt dosing pipe, H2. Ammonium salt dosing pipe, H3. Alkali dosing pipe, F1. First electric valve, F2. Second electric valve; K1. First flowmeter, K2. Second flowmeter, K3. Third flowmeter, K4. Fourth flowmeter; C4. Lifting pump; P1. Orthophosphate online detector, P2. pH value online detector. . DETAILED DESCRIPTION

[0061] The embodiments of the present invention are described in detail below with reference to the accompanying drawings, but the present invention can be implemented in many different ways as defined and covered by the claims.

[0062] Example:

[0063] See also Figure 1 , a method for treating excess sludge, comprising a phosphorus release step and a phosphorus recovery step, the details of which are as follows:

[0064] The phosphorus releasing step comprises the following steps:

[0065] Step S1, sending the phosphorus-rich excess sludge Q1 discharged from the sewage treatment biochemical system to a sludge concentration unit for concentration treatment to obtain concentrated sludge Q3 and supernatant Q2;

[0066] Step S2, sending the concentrated sludge Q4 with a mass or flow rate accounting for 10%-20% to the sludge decomposition unit for decomposition treatment to obtain decomposition-treated sludge; sending the remaining concentrated sludge Q5 to the sludge dehydration unit for sludge dehydration treatment to obtain dry sludge and sludge dehydrated liquid;

[0067] Step S3, circulating the cracked sludge obtained in step S2 to the sludge concentration unit 1 in step S1.

[0068] In this embodiment, step S3 also includes a pH adjustment step, specifically: the sludge after the cracking treatment in step S2 is sent to the pH adjustment unit for pH adjustment to obtain pH-adjusted sludge, and then the pH-adjusted sludge Q6 is circulated to the sludge concentration unit in step S1; the pH control range in the pH adjustment unit is 9-10, and the pH control range is further preferably 9-9.5.

[0069] The phosphorus recovery step specifically comprises:

[0070] The supernatant obtained in step S1 is input into the phosphorus recovery unit 8 for phosphorus recovery treatment to obtain phosphorus crystals and low-phosphorus water. This situation is applicable when the sludge dehydration unit uses aluminum salts, iron salts, magnesium salts and other agents that can form precipitation with phosphate ions, and the sludge dehydration liquid obtained in step S2 does not enter the phosphorus recovery unit, and only the supernatant obtained in step S1 enters the phosphorus recovery unit for phosphorus recovery treatment.

[0071] Alternatively, the supernatant obtained in step S1 and the sludge dewatering liquid obtained in step S2 are input into the phosphorus recovery unit 8 for phosphorus recovery treatment to obtain phosphorus crystals and low-phosphorus water. This situation is applicable when the sludge dewatering unit does not use agents such as aluminum salts, iron salts, and magnesium salts that can form precipitation with phosphate ions.

[0072] See also Figure 2-Figure 3 A method for treating excess sludge includes a phosphorus release mechanism and a phosphorus recovery unit 8. The excess sludge of a municipal sewage treatment plant is subjected to phosphorus release treatment by the phosphorus release mechanism, and then phosphorus is recovered by the phosphorus recovery unit 8, as follows:

[0073] In this embodiment, the phosphorus release mechanism includes a sludge concentration unit 1, a sludge breaking component 2 and a sludge dewatering unit 3. The sludge concentration unit 1 is provided with a residual sludge inlet 1.1, a concentrated sludge discharge outlet 1.2 and a supernatant discharge outlet 1.3; the sludge breaking component 2 includes a sludge breaking unit 2.1 and a pH value adjustment unit 2.2 arranged in series.

[0074] The residual sludge is transported by the residual sludge conveying pipeline 12 (a first flowmeter K1 is provided on the pipeline), and enters the sludge concentration unit 1 through the residual sludge feed port 1.1 for concentration treatment; the supernatant after concentration treatment is discharged through the supernatant discharge port 1.3 to the phosphorus recovery unit 8 for phosphorus recovery treatment; the concentrated sludge after concentration treatment is discharged through the concentrated sludge discharge port 1.2, a part of the concentrated sludge enters the sludge cracking unit 2.1 through the first pipeline 4 (a second flowmeter K2 and a first electric valve F1 are provided on the pipeline) for sludge cracking treatment, and another part of the concentrated sludge enters the sludge dehydration unit 3 through the second pipeline 5 (a third flowmeter K3 and a second electric valve F2 are provided on the pipeline) for sludge dehydration treatment. The flow ratio of the sludge in the two pipelines can be adjusted by controlling the first electric valve F1 and the second electric valve F2; the cracked sludge after cracking treatment enters the pH value adjustment unit 2.2 for pH value adjustment, and then is lifted by the lifting pump C4, and is transported to the residual sludge feed port 1.1 by the third pipeline 6 to circulate to the sludge concentration unit 1. The detailed structure is as follows:

[0075] The sludge thickening unit 1 adopts a circular gravity thickening tank in the prior art. In this embodiment, the tank body is constructed of reinforced concrete or steel anti-corrosion equipment. Sludge is concentrated in an anaerobic environment without stirring in the sludge thickening tank, and anaerobic biological phosphorus release effect occurs simultaneously, releasing phosphorus into the liquid phase. The sludge concentration time in the tank (calculated by hydraulic retention time) is 6-24 hours (preferably 14-24 hours). The residual sludge inlet 1.1 is connected to the residual sludge conveying pipeline 12, and the residual sludge conveying pipeline 12 is connected to the external sludge conveying pump. The sludge flows from the intersection of the residual sludge conveying pipeline 12 and the outlet pipeline of the lifting pump C4 to the residual sludge inlet 1.1 in the sludge concentration unit 1 for no less than 3 seconds; the supernatant discharge port 1.3 arranged on the upper part of the sludge concentration unit 1 is connected to the phosphorus recovery unit 8, and the supernatant (i.e., the high-concentration phosphorus-containing supernatant produced by the sludge concentration tank) is transported to the phosphorus recovery unit for phosphorus recovery treatment; a concentrated sludge discharge port 1.2 is arranged at the bottom of the sludge concentration unit 1, and the concentrated sludge discharge port 1.2 is respectively connected to the sludge breaking component 2 and the sludge dehydration unit 3. When the sludge dehydration unit 3 does not use aluminum salts, iron salts, magnesium salts and other agents that can form precipitates with phosphate ions, the sludge dehydration liquid produced by the sludge dehydration unit and the supernatant discharged from the sludge concentration unit enter the phosphorus recovery unit for phosphorus recovery treatment to obtain phosphorus crystal products and low-phosphorus water; when the sludge dehydration unit 3 uses aluminum salts, iron salts, magnesium salts and other agents that can form precipitates with phosphate ions, the sludge dehydration liquid produced by the sludge dehydration unit does not enter the phosphorus recovery unit, but directly returns to the biochemical pool at the front end of the sewage treatment system; the low-phosphorus water discharged from the phosphorus recovery unit returns to the biochemical pool at the front end of the sewage treatment system.

[0076] The sludge decomposition component 2 includes a sludge decomposition unit 2.1 and a pH value adjustment unit 2.2 arranged in series, see Figure 4 , this embodiment is preferred:

[0077] The sludge decomposition unit 2.1 includes a first shell A1, a first stirring assembly A2, a first sludge inlet pipe A3, a first sludge outlet pipe A4 and a first pH controller A6; the first shell A1 includes a first body A1.2 having a first accommodating chamber A1.1, the first sludge inlet pipe A3 and the first sludge outlet pipe A4 are both arranged on the first body A1.2 and are both connected to the first accommodating chamber A1.1; the first sludge inlet pipe A3 is connected to the concentrated sludge outlet 1.2 of the sludge thickening unit through a first pipeline 4; the first sludge outlet pipe A4 is connected to the pH value adjusting unit through a fourth pipeline 7 2.2 is connected; the first body A1.2 is provided with a first dosing tube A5 connected with the first accommodating chamber A1.1; the first stirring assembly A2 includes a first driving power source A2.1, a first stirring shaft A2.2 and a first stirring blade A2.3, the first driving power source A2.1 is arranged on the first shell A1; the connecting end of the first stirring shaft A2.2 is connected with the output end of the first driving power source A2.1, the free end of the first stirring shaft A2.2 is arranged in the first accommodating chamber A1.1 and the first stirring blade A2.3 is arranged thereon. The first body A1.2 is provided with a measuring hole connected with the first accommodating chamber A1.1, the first pH controller A6 is arranged at the measuring hole for measuring the pH value of the sludge; the first pH controller is connected to an external PLC control system, and the pH controller measures the pH value of the sludge through a first measuring electrode A6.1; the measuring electrode is arranged at the measuring hole and a protective net is arranged on the outside of the measuring electrode.

[0078] Further preferably, the first shell A1 is a cylindrical shell, made of carbon steel anti-corrosion material, and uses sodium hydroxide to break up the sludge. In this embodiment, the pH control range in the sludge breaking component is: 10.8-11, and the reaction time of sludge breaking is: 40-60min. The inner wall of the first accommodating chamber A1.1 is also provided with a plurality of protrusions A1.3 facing the center of the first accommodating chamber; the protrusion A1.3 is a hemispherical protrusion with a radius of 40-80mm; the plurality of protrusions A1.3 are evenly distributed on the inner wall of the first accommodating chamber, where the radius of the hemispherical protrusions is the same, and the plurality of protrusions are evenly distributed on the vertical inner wall of the first accommodating chamber, and the distance between the edges of two adjacent protrusions is 1.5 times their diameters. The first stirring shaft A2.2 is provided with multiple layers of the first stirring blades A2.3 at intervals along its axial direction (here, preferably two layers of first stirring blades are arranged along the up and down directions, and the stirring blades generate upward thrust when rotating); the first body A1.2 is also provided with a first odor collecting pipe A7 for collecting odor generated in the first accommodating chamber; the first shell A1 also includes an opening connected to the first accommodating chamber A1.1, and a removable cover A1.4 is provided at the opening, and the first driving power source A2.1, the first dosing pipe A5, the first pH controller A6 and the first odor collecting pipe A7 are all arranged on the removable cover A1.4.

[0079] In this embodiment, the pH value adjusting unit 2.2 includes a second shell B1, a second stirring assembly B2, a second mud inlet pipe B3 and a second mud outlet pipe B4; the second shell B1 includes a second body B1.2 having a second accommodating chamber B1.1, the second mud inlet pipe B3 and the second mud outlet pipe B4 are both arranged on the second body B1.2 and are both connected to the second accommodating chamber B1.1, the second mud inlet pipe B3 is connected to the first mud outlet pipe A4 through a fourth pipeline 7, and the second mud outlet pipe B4 is connected to the residual sludge through a third pipeline 6 (a lifting pump C4 is provided on the third pipeline). The second body B1.2 is connected to the feed port 1.1; the second dosing tube B5 connected to the second accommodating chamber B1.1 is provided on the second body B1.2; the second stirring assembly B2 includes a second driving power source B2.1, a second stirring shaft B2.2 and a second stirring blade B2.3, and the second driving power source B2.1 is arranged on the second shell B1; the connecting end of the second stirring shaft B2.2 is connected to the output end of the second driving power source B2.1, and the free end of the second stirring shaft B2.2 is arranged in the second accommodating chamber B1.1 and is provided with the second stirring blade B2.3. Further preferably, the second shell B1 is a cylindrical shell; in this embodiment, the control range of the pH value in the pH value adjustment unit 2.2 is 9-10, preferably 9-9.5. The effective volume of the second accommodating chamber B1.1 in the pH value adjusting unit 2.2 is half of the volume of the first accommodating chamber A1.1 in the sludge decomposition unit 2.1, and the height of the pH value adjusting unit 2.2 is lower than the sludge decomposition unit 2.1, which can ensure that the sludge in the sludge decomposition unit 2.1 flows into the pH value adjusting unit 2.2 by gravity. The soluble COD of the sludge discharged from the third pipeline 6 is not less than 2000 mg / L, and the pH is 9-9.5. In addition, the second body B1.2 is provided with a measuring hole connected to the second accommodating chamber B1.1, and the second pH controller B6 is arranged at the measuring hole for measuring the pH value of the sludge; the second pH controller is connected to the external PLC control system, and the pH controller measures the pH value of the sludge through the second measuring electrode B6.1; the measuring electrode is arranged at the measuring hole and a protective net is arranged on the outside of the measuring electrode. The second body B1.2 is also provided with a second odor collection pipe B7 for collecting the odor generated in the second accommodating chamber.

[0080] In this embodiment, the phosphorus recovery unit 8 is connected to the supernatant discharge port 1.3 through a fifth pipeline 9 (a fourth flowmeter K4 is provided on the pipeline); the sludge after the sludge dehydration treatment by the sludge dehydration unit 3 is transported through a dry sludge conveying member 10 (a dry sludge conveying pipe is preferably used here, and a conveying device such as a conveying belt can also be used), and the sludge dehydrated liquid after the sludge dehydration treatment is connected to the fifth pipeline 9 or the phosphorus recovery unit through a sixth pipeline 11. Figure 2-3It is shown in the figure that it enters the phosphorus recovery unit 8 after being connected with the fifth pipeline 9.

[0081] Further preferably, the phosphorus recovery unit 8 comprises an outer shell 8.1, a middle shell 8.2, an inner shell 8.3, a water inlet pipe 8.5, a drain pipe 8.6, a discharge port 8.7, a plug flow stirring assembly 8.8, a folded plate vortex assembly 8.9, a modular vortex assembly 8.10 and a sloping plate assembly 8.11, see Figure 5 , the detailed structure is as follows:

[0082] The outer shell 8.1 comprises a first cylindrical body 8.1.1 and a first conical body 8.1.2 which is wide at the top and narrow at the bottom and closed at the bottom, and the first cylindrical body 8.1.1 is provided with an a accommodating chamber 8.1.3, and the first conical body 8.1.2 is provided with a b accommodating chamber 8.1.4 which is connected with the a accommodating chamber 8.1.3; a water collecting tank 8.4 is provided on the upper part of the a accommodating chamber 8.1.3;

[0083] The middle shell 8.2 comprises a second cylindrical body 8.2.1 and a second conical body 8.2.2 which is wide at the top and narrow at the bottom and has an opening at the lower end, and a c accommodating chamber 8.2.3 is arranged in the second cylindrical body 8.2.1, and a d accommodating chamber 8.2.4 which is connected to the c accommodating chamber 8.2.3 is arranged in the second conical body 8.2.2; the upper end of the second conical body 8.2.2 is located in the a accommodating chamber 8.1.3 and the lower end thereof is located in the b accommodating chamber 8.1.4;

[0084] The inner shell 8.3 comprises a third cylindrical barrel 8.3.1 arranged in the c accommodating chamber 8.2.3, and the third cylindrical barrel 8.3.1 comprises an e accommodating chamber 8.3.2 with openings at both upper and lower ends.

[0085] In the phosphorus recovery unit 8: the e accommodating chamber 8.3.2 forms a first water flow rising channel A; a water flow descending channel B is formed between the inner wall of the second cylindrical barrel 8.2.1 and the outer wall of the third cylindrical barrel 8.3.1; the annular area between the inner wall of the first cylindrical barrel 8.1.1 and the first conical barrel 8.1.2, the outer wall of the second cylindrical barrel 8.2.1 and the second conical barrel 8.2.2 and the water collecting trough 8.4 enclose a second water flow rising channel C; the plug flow stirring assembly 8.8 and the folded plate vortex assembly 8.9 are arranged from top to bottom in the first water flow rising channel A; the modular vortex assembly 8.10 is arranged in the water flow descending channel B; the inclined plate assembly 8.11 is arranged in the second water flow rising channel C; the lower part of the accommodating chamber 8.1.4 forms a crystal aggregation area D, and the discharge port 8.7 is connected to the crystal aggregation area D.

[0086] The water inlet pipe 8.5 is connected to the supernatant discharge port 1.3 through the fifth pipe 9, and the water outlet end of the water inlet pipe 8.5 passes through the side wall of the first columnar barrel 8.1.1 and the side wall of the second columnar barrel 8.2.1 and is inserted into the upper part of the first water flow rising channel A, and the water outlet end of the water inlet pipe 8.5 is lower than the position of the water collecting tank 8.4; the drain pipe 8.6 is connected to the water collecting tank 8.4.

[0087] Further preferably, the plug-flow stirring assembly 8.8 comprises a third driving power source 8.8.1, a third stirring shaft 8.8.2 and a third stirring blade 8.8.3, the connection end of the third stirring shaft 8.8.2 is connected to the output end of the third driving power source 8.8.1, and the third stirring blade 8.8.3 is arranged on the free end of the third stirring shaft 8.8.2; the outlet end of the water inlet pipe 8.5 is located 20-50cm above the third stirring blade 8.8.3. The plug-flow stirring assembly 8.8 lifts the liquid and suspended particles in the first water flow rising channel A from its lower section to the upper section, and provides a driving force for the water flow to circulate in the first water flow rising channel A.

[0088] The top of the folded plate vortex assembly 8.9 is 0.5m away from the lower edge of the third stirring blade 8.8.3 and the lower end is flush with the lower end of the inner shell 8.3; see Figure 6 and Figure 7 The folded plate vortex assembly 8.9 includes a first folded plate 8.9.1 and a second folded plate 8.9.2 arranged in parallel. The first folded plate 8.9.1 includes a plurality of connecting plates connected in sequence, and the angle α between two adjacent connecting plates is 80°-100°; the first folded plate 8.9.1 and the second folded plate 8.9.2 are mirror images. The angle α between adjacent connecting plates in the folded plate vortex assembly is 90°, and the length Q1 of the connecting plate is 20% of the diameter of the inner shell 8.3. The angle and length of each connecting plate in the same first folded plate or second folded plate are the same, and the crests and troughs of the first folded plate and the second folded plate are horizontally aligned, and the horizontal spacing Q2 is equal and is 10% of the diameter of the inner shell 8.3.

[0089] The upper end of the modular vortex component 8.10 is located 0.5m below the inner cavity liquid level of the water flow descending channel B, and the lower end is 0.6m away from the plane where the lower end of the inner shell 8.3 is located. Figure 8 , Fig. 9 , Fig.10As shown, the modular eddy current assembly has an outer shape of a fan ring cylindrical cube, and its horizontal projection is a fan ring shape, including a plurality of eddy current monomers stacked or spaced, and the eddy current monomer is a hollow columnar body surrounded by a first vertical plate 8.10.1, a second vertical plate 8.10.2, an upper arc-shaped outer frame 8.10.3, an upper arc-shaped inner frame 8.10.4, a lower arc-shaped outer frame 8.10.5, and a lower arc-shaped inner frame 8.10.6, and a eddy current sheet is installed in the eddy current monomer, and the cross section of the eddy current sheet is at least one of a triangle, a semicircle, and a rectangle. The columnar body is made of metal or engineering plastic material, and can bear the weight of the frame itself and the eddy current sheet installed inside.

[0090] In this embodiment, it is further preferred that the vortex monomer is provided with a semicircular shell vortex layer and an isosceles right-angled triangle vortex layer alternately formed, the projection of the semicircular shell vortex layer in the horizontal direction is an arc shape, and its cross-sectional shape is a semicircle with a diameter of 30-40mm. The horizontal spacing of each semicircular shell vortex sheet Y in the same layer is equal, and the distance between two adjacent semicircular shell vortex sheets is 1.3 times its diameter; the length of the isosceles right-angled triangle vortex sheet S in the same layer is determined by the radius of its own horizontal projection arc and the arc radian corresponding to the horizontal projection of the frame of the vortex monomer, and the projection of a single isosceles right-angled triangle vortex sheet in the horizontal direction is an arc shape, and its cross-sectional shape is an isosceles right-angled triangle, and the height of the triangle is the same as the radius of the semicircular shell vortex sheet. Two adjacent layers of semicircular shell vortex sheets and isosceles right-angled triangle vortex sheets are arranged alternately, and the projections of two adjacent layers of semicircular shell vortex sheets and isosceles right-angled triangle vortex sheets on the horizontal plane do not overlap.

[0091] The inclined plate assembly 8.11 includes a plurality of settling inclined plates arranged in parallel, and the settling inclined plates are arranged at an angle with the inner wall of the a accommodating chamber; and the inclined plate assembly 8.11 is located in the middle and lower part of the a accommodating chamber.

[0092] The water inlet pipe 8.5 includes a horizontal pipe section, an arc-shaped transition pipe section and a vertical pipe section arranged in series, the horizontal pipe section passes through the upper part of the outer shell 8.1 and the middle shell 8.2, the arc-shaped transition pipe section is a pipe section bent downward by 90 degrees and extends to the upper part of the inner shell 8.3, and the outlet of the vertical pipe section is located 0.4 meters above the third stirring blade 8.8.3 in the plug-flow stirring assembly 8.8. A pipeline mixer H is installed on the horizontal pipe section of the water inlet pipe 8.5, and the pipeline mixer H is connected to the magnesium salt dosing pipe H1, the ammonium salt dosing pipe H2 and the alkali dosing pipe H3.

[0093] In this embodiment, the sludge dewatering unit 3 adopts the existing horizontal spiral centrifugal dewatering equipment.

[0094] In addition, a control system is also provided in this embodiment, which includes online detection instruments, cables and an electric control cabinet containing a programmable logic controller (PLC). The online detection instruments include a first flow meter K1 arranged on the residual sludge conveying pipeline 12, a second flow meter K2 arranged on the first pipeline 4, a third flow meter K3 arranged on the second pipeline 5, a fourth flow meter K4 arranged on the fifth pipeline 9, an orthophosphate online detector P1 arranged near the supernatant discharge pipe, an online pH value detector P2 arranged in the phosphorus recovery unit 8, and a first pH controller A6 and a second pH controller B6 arranged in the sludge decomposition component; the cables and the electric control cabinet containing the programmable logic controller (PLC) all adopt existing mature equipment, which can power the online detection instruments and communicate with the online detection instruments. The PLC controls the operation of external dosing equipment and other equipment according to the data detected by the online monitoring instruments and the preset control logic.

[0095] The technical solution of this embodiment is specifically:

[0096] The phosphorus-rich residual sludge (Q1 residual, water content 99.2%) discharged from the sewage treatment biochemical system is mixed with the post-destruction sludge (Q6 post-destruction) discharged from the sludge destructing unit 2.1 through the residual sludge conveying pipeline 12 and then enters the sludge concentration unit 1. The phosphorus-rich residual sludge is concentrated in the sludge concentration unit 1 under the action of the carbon source provided by the post-destruction sludge and simultaneously undergoes anaerobic biological phosphorus release effect, releasing phosphorus in the solid phase into the liquid phase. The low-phosphorus sludge after concentration and biological phosphorus release is discharged from the bottom of the gravity concentration tank. A part of the concentrated sludge (Q4 destructed) enters the sludge destructing unit 2.1 in the sludge destructing component 2 through the first pipeline 4 for sludge destructing. After the destructing is completed, the sludge enters the pH value adjustment unit 2.2 for pH adjustment and then all returns to the sludge concentration unit 1; the other part of the concentrated sludge (Q5 dehydrated) is discharged into the sludge dehydration unit 3 through the second pipeline 5 for dehydration treatment. In this embodiment, the flow rate or mass ratio Q4 breaking of the total amount of sludge entering the sludge breaking unit and the concentrated sludge is: (Q4 breaking + Q5 dehydration) = 0.2; the high-concentration phosphorus-containing supernatant produced by the sludge concentration unit 1 is discharged into the phosphorus recovery unit 8 through the fifth pipeline 9 to recover phosphorus; the sludge dehydration liquid produced by the sludge dehydration unit is mixed with the supernatant of the sludge concentration unit through the sixth pipeline 11 and discharged into the phosphorus recovery unit 8 for phosphorus recovery, and the dry sludge is transported out for disposal through the dry sludge conveying part 10; the low-phosphorus water discharged from the phosphorus recovery unit is returned to the biochemical pool at the front end of the sewage treatment system through the seventh pipeline 13.

[0097] In this embodiment, the sludge decomposition unit uses alkali (NaOH or KOH) to stir at room temperature to decompose the concentrated sludge, and the mass ratio of the sludge discharged into the sludge decomposition unit to the total amount of concentrated sludge is: 10%-20%. The amount of alkali added to the sludge decomposition unit is controlled by pH, and the decomposition pH is: 10.8-11.5. The reaction time of sludge decomposition is 20-100min, preferably 40-120min. After alkali decomposition, the sludge releases COD (carbon source), ammonia nitrogen, organic nitrogen, orthophosphate, organic phosphorus and other substances into the aqueous phase. The concentration of soluble COD in the decomposition sludge is not less than 2000mg / L. After acid is added to adjust the pH to 9-10 (preferably 9-9.5), it is converted into decomposition sludge; the mass of the decomposition sludge is equal to the mass of the concentrated sludge plus the reagent added during the decomposition process, and it is mixed with the phosphorus-rich residual sludge discharged from the sewage treatment biochemical system and discharged into the gravity concentration tank. The sludge decomposition step in this embodiment simultaneously achieves five technical effects:

[0098] ① The residual phosphorus in the sludge was broken and released, and orthophosphate was released from the solid phase to the liquid phase, which further increased the amount of phosphorus released from the sludge and further improved the phosphorus recovery rate;

[0099] ② The high-concentration COD (carbon source) released by sludge cracking is returned to the sludge thickening tank as a carbon source for anaerobic biological phosphorus release of the remaining sludge. No external carbon source is needed, which realizes "waste treatment with waste" and saves the cost of sludge phosphorus release;

[0100] ③ Sludge cracking releases ammonia nitrogen, reducing the amount of ammonium salt (such as ammonium chloride) added to the subsequent phosphorus recovery unit to recover struvite, further saving the cost of phosphorus recovery;

[0101] ④ After the sludge is cracked, the dewatering performance can be improved, and the amount of sludge dewatering agent added in the subsequent sludge dewatering unit can be reduced, which is beneficial to improving the treatment efficiency of the subsequent sludge dewatering unit and reducing the cost of sludge dewatering;

[0102] ⑤ The pH of the cracked sludge is adjusted to 9-10 (preferably 9-9.5) by adding acid, and then mixed with the remaining sludge. In this embodiment, the pH of the mixed sludge entering the sludge thickening tank can be between 8-9, forming the most suitable pH for anaerobic biological phosphorus release in the sludge thickening tank.

[0103] Table 1 Main components of sludge before and after sludge concentration

[0104]

[0105] Note: The sludge concentration before concentration (Q1 residue, which refers to the residue sludge entering the sludge concentration unit through the residue sludge conveying pipeline 12) in the table is MLSS=8g / L, and the sludge concentration after sludge concentration and decomposition (Q6 decomposition) is MLSS=20g / L. In this embodiment, the volume of the sludge after sludge concentration and decomposition (Q6 decomposition) is only about 8% of the volume of the residue sludge Q1 residue entering the sludge concentration tank through the residue sludge conveying pipeline. The composition data of the sludge are all measured by centrifuging the sludge and taking the supernatant.

[0106] The excess sludge before concentration (Q1 excess) and the sludge after cracking (Q6 after cracking) are mixed before entering the sludge concentration unit 1 and then enter the sludge concentration unit 1. Compared with the conventional gravity concentration process, this embodiment not only realizes the physical concentration of sludge in the sludge concentration unit 1, but also realizes the following technical effects:

[0107] ① The excess sludge (Q1 excess) and the cracked sludge (Q6 cracked) are mixed before entering the sludge concentration unit. The mixing process and pipeline transportation process can enable the microorganisms in the excess sludge (Q1 excess) to quickly adsorb the organic components in the cracked sludge (Q6 cracked), creating conditions for the microorganisms to further absorb the adsorbed organic matter into the microbial cells in the concentration tank, overcoming the defect of low mass transfer efficiency between organic matter and microbial cells caused by small fluid disturbance in the sludge concentration tank, and allowing more organic components in the cracked sludge to enter the microbial cells in the excess sludge to achieve anaerobic phosphorus release;

[0108] ② Phosphorus-rich microorganisms (such as polyphosphate bacteria) in the residual sludge release the phosphorus in the cells into the water (in the form of orthophosphate, PO4 3- The anaerobic biological phosphorus release of the entire amount of excess sludge was achieved, creating conditions for subsequent phosphorus recovery;

[0109] ③ The organic nitrogen and organic phosphorus contained in the cracked sludge are converted into ammonia nitrogen and orthophosphate (PO4 3- ), the conversion of organic nitrogen into ammonia nitrogen can save the dosage of ammonia nitrogen in the subsequent phosphorus recovery unit, and the conversion of organic phosphorus into orthophosphate can further improve the phosphorus recovery efficiency (organic phosphorus cannot be recovered through struvite crystallization).

[0110] The test data of the main components of the supernatant before sludge concentration, at the water inlet of the sludge concentration unit, and at the effluent of the sludge concentration unit are shown in Table 2. This embodiment has a significant effect on phosphorus release from sludge, and most of the phosphorus exists in the form of orthophosphate, which can be recovered by the subsequent phosphorus recovery unit 8.

[0111] Table 2 Main components of sludge before sludge thickening, sludge thickening tank inlet, and sludge thickening tank effluent

[0112]

[0113] Note: The sludge concentration MLSS in the table before sludge concentration (Q1 residue, refers to the residual sludge entering the sludge concentration unit from the residual sludge conveying pipeline 12) is 8g / L. The data before sludge concentration is the data measured by centrifuging the sludge and taking the supernatant; the sludge concentration of the mixed liquor at the inlet of the sludge concentration tank is about 8.8g / L. In this embodiment, the volume of the sludge after concentration is 40% of the volume of the sludge before concentration (Q1 residue), the concentrated sludge entering the cracking unit (Q4 cracking) accounts for 20% of the total volume of the concentrated sludge (Q4 cracking + Q5 dehydration), the reagent NaOH added to the sludge cracking unit is added in solid form, the density of the sludge after cracking is similar to that of the sludge before cracking (Q4 cracking), and the volume of the sludge after cracking (Q6 cracking) accounts for 8% of the volume of the sludge before concentration (Q1 residue); the composition of the mixed liquor at the inlet of the sludge concentration tank is measured by taking the supernatant obtained by centrifuging the mixed liquor.

[0114] The phosphorus recovery unit 8 described in this embodiment uses magnesium ammonium phosphate crystals (struvite) to recover phosphorus in the liquid phase. The wastewater containing orthophosphate from the sludge concentration unit 1 and the sludge dehydration unit 3 is mixed with the reagent (the reagent is magnesium chloride, ammonium chloride, and sodium hydroxide) in the pipeline mixer H and then enters the phosphorus recovery unit 8. The dosage of magnesium chloride and ammonium chloride reagents is based on Mg:NH4 + : P = 1.3:1.3:1 (molar ratio), the pH of the crystallization reaction is controlled at 9.5-10, the third stirring blade rotates to generate an upward thrust, stirs and mixes the liquid and the suspended particles, and causes the liquid mixture to circulate.

[0115] The orthophosphate in the influent water and the crystal-forming ions (magnesium ions, ammonium ions) in the reagent are contacted and mixed under the mechanical stirring condition of the third stirring blade to form tiny magnesium ammonium phosphate crystals (crystal nuclei). The tiny crystals circulate in the first water flow ascending channel A and the water flow descending channel B along with the water flow. When passing through the folded plate vortex component 8.9 and the modular vortex component 8.10, the crystal-forming ions in the wastewater are further contacted and mixed under the action of a large number of micro-vortices generated by the vortex component, and the tiny crystal particles are fluidized. The tiny crystals and the crystal nuclei and the crystal-forming ions fully collide and contact with each other under the action of the micro-vortices. , secondary nucleation occurs, and self-induced crystallization is achieved without the need for adding crystal seeds. The particle size of the crystal particles gradually increases. When the particle size and mass of the crystal particles increase to a certain extent, under the action of gravity, the large crystal particles gradually separate from the circulating water flow and flow into the crystal gathering area D. After the crystallization is completed, the water flow enters the annular solid-liquid separation area. The fine crystal particles entrained in the water flow are further separated from the solid and liquid under the action of gravity and the inclined plate assembly. After the crystal particles are precipitated, they slide to the crystal gathering area D under the action of gravity. The supernatant after precipitation is collected upward to the water collection tank 8.4 and discharged from the phosphorus recovery unit 8 through the drain pipe 8.6. The struvite crystals accumulated in the crystal gathering area D are regularly discharged to the dehydration and separation equipment set separately through the discharge port 8.7. In this embodiment, the recovery rate of orthophosphate by the phosphorus recovery unit is greater than 80%, and the recovered product is struvite.

[0116] The low-phosphorus liquid discharged from the phosphorus recovery unit is returned to the biochemical pool at the front end of the sewage treatment system through the seventh pipeline 13.

[0117] In this embodiment, the sludge dewatering unit adopts existing conventional sludge dewatering technology and equipment (such as a horizontal screw centrifugal dewatering machine) to dewater the concentrated sludge. During the dehydration process, no aluminum salt, iron salt or other agent that can form a precipitate with phosphate ions is added, and only a small amount of polyacrylamide is added. The sludge dewatering liquid is returned to the phosphorus recovery unit to recover phosphorus, and the dehydrated dry sludge is transported out for separate disposal.

[0118] Applying the technical solution of this embodiment has the following beneficial effects:

[0119] 1. Existing sludge decomposition and phosphorus release technologies all use the method of decomposing the entire amount of excess sludge. In this embodiment, only 10%-20% of the concentrated sludge needs to be decomposed by adding alkali, and the COD (organic component) released by the decomposition is used as the carbon source for the polyphosphate microorganisms (polyphosphate bacteria) in the entire amount of excess sludge entering the thickening tank. Anaerobic phosphorus release occurs in the anaerobic environment of the sludge thickening tank without the need for an external carbon source. The new scheme of alkaline phosphorus release of a small amount of concentrated sludge + anaerobic biological phosphorus release of the entire amount of excess sludge achieves low-cost and efficient phosphorus release from the entire amount of excess sludge. In this embodiment, the equipment investment and operating costs (drug consumption, electricity consumption) of the sludge breakdown unit are only equivalent to 10%-20% of the existing full-volume sludge alkaline phosphorus decomposition process, and the equipment footprint can also be saved; the addition of the broken sludge can shorten the anaerobic biological phosphorus release time of the remaining sludge in the gravity thickening tank to 6 hours, which is only 1 / 80 of the time required for the traditional sludge anaerobic digestion process (anaerobic digestion time 20-30 days), greatly reducing the equipment investment and operating costs of sludge phosphorus release and phosphorus recovery.

[0120] 2. Some of the phosphorus and nitrogen elements released into the liquid phase by the existing physical phosphorus decomposition (ultrasound, thermal hydrolysis, mechanical ball milling) and chemical phosphorus decomposition (acid, alkali) technologies exist in the form of organic phosphorus and organic nitrogen, and organic phosphorus is difficult to recycle. In this embodiment, the sludge after alkaline decomposition is returned to the thickening tank. The organic phosphorus and organic nitrogen released during the sludge decomposition process are converted into orthophosphate and ammonia nitrogen that can be recovered by the subsequent phosphorus recovery unit under the action of the anaerobic environment of the thickening tank and anaerobic microorganisms in the residual sludge, which can further improve the phosphorus recovery rate and reduce the cost of adding ammonia nitrogen to the phosphorus recovery unit.

[0121] 3. At present, most of the domestic urban sewage treatment plants adopt the technical route of sludge gravity concentration + sludge dewatering for the treatment of residual sludge, and have built sludge concentration tanks and sludge dewatering facilities. In this embodiment, the gravity concentration tank adopts the existing conventional gravity concentration tank. When it is necessary to recover phosphorus from the residual sludge of the existing sewage treatment plant, it is only necessary to add a sludge breaking component (only 10%-20% of the total concentrated sludge needs to be broken, and there is no need to break the entire amount of concentrated sludge), a sludge phosphorus recovery device, and a control system. The pipelines are modified accordingly to economically and conveniently realize the recovery of sludge phosphorus resources in the existing sewage treatment plants.

[0122] 4. In this embodiment, the phosphorus recovery unit is equipped with an outer shell, a middle shell, and an inner shell to form a circulating flow channel formed by a first water flow rising channel, a water flow descending channel, and a second water flow rising channel. The plug flow stirring component and the folded plate vortex component are arranged from top to bottom in the first water flow rising channel and combined with the modular vortex component in the water flow descending channel, forming a mechanical stirring mixed crystallization + hydraulic vortex crystallization composite system. Due to its special structure, hydraulic classification is achieved during operation, so that the solution is fully mixed with materials and the crystal particles are fluidized, and self-induction is achieved without the need for external crystal seeds. The crystal particles are larger in size and purity than those in traditional stirred crystallization. The first water flow ascending channel and the water flow descending channel form a water flow circulation channel to automatically sort the crystal particles. Particles with large size and mass will automatically separate from the circulating water flow and be discharged into the crystal gathering area under the action of gravity, while crystal particles with small size and mass continue to crystallize in the water flow circulation channel. The crystal particles collected in the crystal gathering area are larger in size and higher in purity than those in traditional stirred crystallization. The inclined plate assembly is arranged in the second water flow ascending channel to perform secondary separation on the fine crystal particles entrained in the water flow, thereby further improving the recovery efficiency of the phosphorus crystal particles.

[0123] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for treating excess sludge, characterized in that: including a phosphorus release step; The phosphorus releasing step comprises the following steps: Step S1, sending the phosphorus-rich excess sludge (Q1) to the sludge concentration unit (1) for concentration treatment to obtain concentrated sludge (Q3) and supernatant (Q2); Step S2, sending the concentrated sludge (Q4) with a mass or flow rate ratio of 10%-20% to the sludge decomposition unit (2.1) for decomposition treatment to obtain decomposition-treated sludge; sending the remaining concentrated sludge (Q5) to the sludge dehydration unit (3) for sludge dehydration treatment to obtain dry sludge and sludge dehydrated liquid; Step S3, circulating the cracked sludge obtained in step S2 to the sludge concentration unit (1) in step S1.

2. The method for treating excess sludge according to claim 1, characterized in that: The step S3 also includes a pH adjustment step, which specifically comprises: sending the sludge after the cracking treatment in step S2 to a pH adjustment unit (2.2) for pH adjustment to obtain pH-adjusted sludge, and then circulating the pH-adjusted sludge (Q6) to the sludge concentration unit in step S1; the pH value in the pH adjustment unit (2.2) is controlled within a range of 9-10; the pH value in the sludge cracking unit is controlled within a range of 10.8-11.5; the cracked sludge in step S3 is mixed with the residual sludge rich in phosphorus and then transported to the sludge concentration unit via a pipeline for a flow time of not less than 3 seconds.

3. The method for treating excess sludge according to claim 2, characterized in that: The concentration time of the phosphorus-rich excess sludge in the sludge concentration unit is 6-24 hours; the reaction time of the sludge decomposition unit for decomposition treatment is 20-100 minutes; the control range of the pH value in the pH adjustment unit is 9-9.5; the pH value of the decomposition-treated sludge mixed with the phosphorus-rich excess sludge in step S3 is 8-9.

4. The method for treating excess sludge according to claim 2, characterized in that: It also includes a phosphorus recovery step, specifically including: The supernatant obtained in step S1 is input into a phosphorus recovery unit (8) for phosphorus recovery treatment to obtain phosphorus crystals and low-phosphorus water; Alternatively, the supernatant obtained in step S1 and the sludge dehydrated liquid obtained in step S2 are input into a phosphorus recovery unit (8) for phosphorus recovery treatment to obtain phosphorus crystals and low-phosphorus water.

5. The method for treating excess sludge according to any one of claims 2 to 4, characterized in that: The sludge concentration unit (1) is a gravity concentration tank; the sludge concentration unit (1) is provided with a residual sludge inlet (1.1), a concentrated sludge outlet (1.2) and a supernatant outlet (1.3); the residual sludge inlet (1.1) is connected to a residual sludge conveying pipeline (12); The sludge decomposition unit (2.1) comprises a first shell (A1), a first stirring assembly (A2), a first sludge inlet pipe (A3) and a first sludge outlet pipe (A4); The first shell (A1) comprises a first body (A1.2) having a first accommodating chamber (A1.1); the first mud inlet pipe (A3) and the first mud outlet pipe (A4) are both arranged on the first body (A1.2) and are both connected to the first accommodating chamber (A1.1); the first mud inlet pipe (A3) is connected to the concentrated sludge outlet (1.2) of the sludge concentration unit through a first pipeline (4); the first mud outlet pipe (A4) is connected to the pH value adjustment unit (2.2) through a fourth pipeline (7); The first body (A1.2) is provided with a first drug adding pipe (A5) which is in communication with the first containing cavity (A1.1); The first stirring component (A2) includes a first driving power source (A2.1), a first stirring shaft (A2.2) and a first stirring blade (A2.3), wherein the first driving power source (A2.1) is arranged on the first shell (A1); the connecting end of the first stirring shaft (A2.2) is connected to the output end of the first driving power source (A2.1), and the free end of the first stirring shaft (A2.2) is arranged in the first accommodating cavity (A1.1) and the first stirring blade (A2.3) is arranged thereon.

6. The method for treating excess sludge according to claim 5, characterized in that: It also includes a first pH controller (A6); a measuring hole connected to the first containing cavity (A1.1) is provided on the first body (A1.2); the first pH controller is arranged at the measuring hole for measuring the pH value of the sludge; the first pH controller is connected to an external PLC control system, and the first pH controller measures the pH value of the sludge through a first measuring electrode (A6.1); the first measuring electrode is arranged at the measuring hole and a protective net is provided on the outer side of the measuring electrode.

7. The method for treating excess sludge according to claim 5, characterized in that: The inner wall of the first accommodating cavity (A1.1) is also provided with a plurality of protrusions (A1.3) facing the center of the first accommodating cavity; the protrusions (A1.3) are hemispherical protrusions with a radius of 40-80 mm; the plurality of protrusions (A1.3) are evenly distributed on the inner wall of the first accommodating cavity; The first stirring shaft (A2.2) is provided with multiple layers of the first stirring blades (A2.3) at intervals along its axial direction; The first body (A1.2) is also provided with a first odor collecting pipe (A7) for collecting odor generated in the first accommodating chamber; the first shell (A1) also includes an opening connected to the first accommodating chamber (A1.1), and a detachable cover (A1.4) is provided at the opening; the first driving power source (A2.1), the first dosing pipe (A5), the first pH controller (A6) and the first odor collecting pipe (A7) are all arranged on the detachable cover (A1.4).

8. The method for treating excess sludge according to claim 4, characterized in that: The pH value adjustment unit (2.2) comprises a second shell (B1), a second stirring assembly (B2), a second mud inlet pipe (B3) and a second mud outlet pipe (B4); The second shell (B1) comprises a second body (B1.2) having a second accommodating chamber (B1.1); the second mud inlet pipe (B3) and the second mud outlet pipe (B4) are both arranged on the second body (B1.2) and are both connected to the second accommodating chamber (B1.1); the second mud inlet pipe (B3) is connected to the first mud outlet pipe (A4) through a fourth pipe (7), and the second mud outlet pipe (B4) is connected to the residual sludge inlet (1.1) through a third pipe (6); The second body (B1.2) is provided with a second drug adding pipe (B5) communicating with the second accommodating cavity (B1.1); The second stirring component (B2) includes a second driving power source (B2.1), a second stirring shaft (B2.2) and a second stirring blade (B2.3), wherein the second driving power source (B2.1) is arranged on the second shell (B1); the connecting end of the second stirring shaft (B2.2) is connected to the output end of the second driving power source (B2.1), and the free end of the second stirring shaft (B2.2) is arranged in the second accommodating cavity (B1.1) and the second stirring blade (B2.3) is provided thereon.

9. The method for treating excess sludge according to claim 4, characterized in that: The phosphorus recovery unit (8) comprises an outer shell (8.1), a middle shell (8.2), an inner shell (8.3), a water inlet pipe (8.5), a drain pipe (8.6), a discharge port (8.7), a plug-flow stirring assembly (8.8), a folded plate vortex assembly (8.9), a modular vortex assembly (8.10) and an inclined plate assembly (8.11); The outer shell (8.1) comprises a first columnar cylinder (8.1.1) and a first conical cylinder (8.1.2) which is wide at the top and narrow at the bottom and closed at the bottom, wherein an a accommodating chamber (8.1.3) is arranged in the first columnar cylinder (8.1.1), and a b accommodating chamber (8.1.4) which is connected to the a accommodating chamber (8.1.3) is arranged in the first conical cylinder (8.1.2); a water collecting tank (8.4) is arranged at the upper part of the a accommodating chamber (8.1.3); The middle shell (8.2) comprises a second cylindrical body (8.2.1) and a second conical body (8.2.2) which is wide at the top and narrow at the bottom and has an opening at the lower end. A c accommodating chamber (8.2.3) is arranged in the second cylindrical body (8.2.1), and a d accommodating chamber (8.2.4) which is connected to the c accommodating chamber (8.2.3) is arranged in the second conical body (8.2.2); the upper end of the second conical body (8.2.2) is located in the a accommodating chamber (8.1.3) and the lower end thereof is located in the b accommodating chamber (8.1.4); The inner shell (8.3) comprises a third cylindrical body (8.3.1) arranged in the c accommodating chamber (8.2.3), and the third cylindrical body (8.3.1) comprises an e accommodating chamber (8.3.2) with openings at both upper and lower ends; The e accommodating chamber (8.3.2) forms a first water flow ascending channel (A); a water flow descending channel (B) is formed between the inner wall of the second columnar cylinder (8.2.1) and the outer wall of the third columnar cylinder (8.3.1); the first columnar cylinder (8.1.1) and the inner wall of the first conical cylinder (8.1.2), the annular area between the outer wall of the second columnar cylinder (8.2.1) and the second conical cylinder (8.2.2) and the water collecting tank (8.4) form a second water flow ascending channel (C); the plug-flow stirring assembly (8.8) and the folded plate vortex assembly (8.9) are arranged from top to bottom in the first water flow ascending channel (A); the modular vortex assembly (8.10) is arranged in the water flow descending channel (B); the inclined plate assembly (8.11) is arranged in the second water flow ascending channel (C); the lower part of the accommodating chamber (8.1.4) forms a crystal aggregation area (D); The water inlet pipe (8.5) is connected to the supernatant discharge port (1.3), and the water inlet pipe (8.5) penetrates the side wall of the first columnar barrel (8.1.1) and the side wall of the second columnar barrel (8.2.1) and is inserted into the upper part of the first water flow rising channel (A), and the water outlet end of the water inlet pipe (8.5) is lower than the position of the water collecting tank (8.4); the drainage pipe (8.6) is connected to the water collecting tank (8.4); and the discharge port (8.7) is connected to the crystal aggregation area (D).

10. The method for treating excess sludge according to claim 9, characterized in that: The plug-flow stirring assembly (8.8) comprises a third driving power source (8.8.1), a third stirring shaft (8.8.2) and a third stirring blade (8.8.3); the connection end of the third stirring shaft (8.8.2) is connected to the output end of the third driving power source (8.8.1), and the third stirring blade (8.8.3) is arranged on the free end of the third stirring shaft (8.8.2); the water outlet end of the water inlet pipe (8.5) is located 20-50 cm above the third stirring blade (8.8.3); The folded plate vortex component (8.9) is located directly below the plug-flow stirring component (8.8), and the folded plate vortex component (8.9) comprises a first folded plate (8.9.1) and a second folded plate (8.9.2) arranged in parallel, the first folded plate (8.9.1) comprises a plurality of connecting plates connected in sequence, and the angle α between two adjacent connecting plates is 80°-100°; the first folded plate (8.9.1) and the second folded plate (8.9.2) are in a mirror image structure; The modular vortex assembly (8.10) comprises a plurality of vortex monomers stacked or spaced apart, wherein the vortex monomer is a hollow columnar body formed by a first vertical plate (8.10.1), a second vertical plate (8.10.2), an upper arc-shaped outer frame (8.10.3), an upper arc-shaped inner frame (8.10.4), a lower arc-shaped outer frame (8.10.5) and a lower arc-shaped inner frame (8.10.6); a vortex sheet is installed in the vortex monomer, and the cross-section of the vortex sheet is at least one of a triangle, a semicircle and a rectangle; The inclined plate assembly (8.11) comprises a plurality of settling inclined plates arranged in parallel, the settling inclined plates being arranged at an angle to the inner wall of the a accommodating chamber; and the inclined plate assembly (8.11) is located in the middle and lower part of the a accommodating chamber.

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